The present application claims priority to Japanese Application No. P2000-243997 filed Aug. 7, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to printers and printer heads. More specifically, the present invention relates to a printer, a printer head, and a method for fabricating a printer head of a thermal method ink-jet printer. In the present invention, a heater element is arranged so as to overlie a wiring pattern layer carried by a semiconductor substrate, or a wiring pattern portion for power supplying or a wiring pattern portion for grounding, the wiring pattern portions being carried by a semiconductor substrate. This allows heat of the heater element to be efficiently transferred to a liquid ink chamber, even when a driving circuit is formed with multi-layer wiring.
2. Description of the Related Art
In recent years, there are growing needs for colorization of hard copies in the field of, for example, image processing. In response to the needs, conventionally, methods of colorizing hard copies are proposed, such as a dye sublimation method, thermal wax transfer method, inkjet method, electrophotography method, and thermally processed silver process.
In the inkjet method, dots are formed in such a manner that droplets of a recording liquid (ink) are ejected from nozzles provided in a recording head and are attached to a recording medium, allowing output of high-quality images with a simple configuration. The inkjet method is categorized, by the difference of technologies of ejecting ink, into an electrostatic attraction method, continuous oscillation generating method (piezoelectric method), thermal method, and the like.
In the thermal method, ink is locally heated to generate bubbles causing ink to be pushed out from outlets and splashed onto a printing medium, which allows for printing of colored images with a simple configuration.
A printer employing the thermal method is provided with the so-called a printer head that includes, for example, a heater element for heating ink, a driving circuit of a logic integrated circuit for actuating the heater element.
Referring now to FIG. 6, such a conventional printer head is illustrated in a partial sectional view. In a printer head 1, element isolation regions (LOCOS: Local oxidation of silicon) 3 for isolating a transistor are formed at a p-type silicon substrate 2. In a transistor forming region left between the element isolation regions 3 are provided a gate oxide film and the like, so that a MOS (Metal Oxide Semiconductor) switching transistor 4 is formed.
Further, over predetermined spots of the element isolation regions 3 is deposited HfB2, TaAl, or the like by sputtering, or heater element material such as polysilicon by CVD. This forms a resistance film locally, thereby providing a heater element 5 for heating ink.
In the printer head 1, the switching transistor 4 and the heater element 5 are provided with a wiring pattern 8 made of Al or the like, so that the heater element 5 is connected with the switching transistor 4 for actuating the heater element 5.
Subsequently, insulation material such as SiO2 or SiN is deposited to form an insulating layer 9, and a Ta film is then deposited locally above the heater element 5 to provide an anti-cavitation layer 7. Next, a dry film 11, made of a resin or the like, and an orifice plate 12 are sequentially deposited. Further, a liquid ink chamber 14 having an orifice 13 that is a minute outlet in the orifice plate 12, a flow channel for introducing ink into the liquid ink chamber 14, and the like are formed above the heater element 5.
In the printer head 1, ink is introduced into the liquid ink chamber 14 and heat is generated at the heater element 5 by switching operation of the switching transistor 4, thereby heating the ink locally. This heating generates nucleus bubbles over a surface of the heater element 5, and the nucleus bubbles combine and grow into a film bubble. In the printer head 1, the increase in the bubble pressure causes ink to be pushed out of the orifice 13 and to be splashed onto a printing media. Thus, in a printer with the printer head 1, creation of a desired image is achieved by selectively heating the heater element 5 so that ink is intermittently attached onto a printing media.
In the printer head 1, the switching transistor 4 for energizing the heater element is controlled by a logic integrated circuit including a MOS transistor or bipolar transistor. Such a logic integrated circuit is fabricated concurrently with the switching transistor 4 on the semiconductor substrate 2, whereby the heater elements (only one heater element 5 is shown) can be arranged at a high density. This arrangement, therefore, is adapted to secure energizing the heater element by a corresponding switching transistor.
In order to gain a high-quality image, it is necessary to arrange the heater elements at a high density. That is, to provide, for example, an equivalent quality to 600 DPI, the heater elements needs to be arranged at intervals of 42.333 xcexcm. However, it is extremely difficult to provide a discrete driving element for each of the heater elements arranged in such a high-density. In the printer head 1, therefore, the switching transistor and the like are fabricated above the semiconductor substrate and are connected to the corresponding heater element 5 by an integrated circuit technology. In addition, the driving circuit formed above the same semiconductor substrate performs driving of each switching transistor. This arrangement can simplify and secure energizing each heater element 5.
In order to perform printing at a higher printing rate and higher resolution, a driving circuit for driving a switching transistor also needs to be improved in the printing rate and performance. To this end, forming a driving circuit of a printer head with multi-layer wiring using aluminum, which is conductive material, is envisaged to improve the operating rate.
With such an arrangement, however, the distance from the heater element 5 to the liquid ink chamber 14 is increased, which poses a problem of inefficient heat transfer from the heater element 5 to the liquid ink chamber 14. That is, when the driving circuit is formed with one-layer wiring, the interlayer thickness on the heater element 5 is about 0.2 to 0.6 xcexcm. In contrast, when the wiring is formed by adding another layer, the interlayer thickness on the heater element 5 is increased by about 1 to 1.6 xcexcm. Such an increase in the interlayer thickness on the heater element 5 results in inefficient heat transfer from the heater element 5 to the liquid ink chamber, thus requiring greater power supply to actuate the heater element 5. This can also impair the reliability of the heater element 5.
In view of the foregoing, an object of the present invention is to provide a printer, a printer head, and a method for fabricating a printer head, which allow efficient heat transfer from a heater element to a liquid ink chamber.
Another object of the present invention is to provide a printer, a printer head, which allow efficient heat transfer, even when a driving circuit is formed with multi-layer wiring.
To this end, according to one aspect of the present invention, there are provided a printer, a printer head, or a method for fabricating a printer head wherein heater elements are arranged at a layer overlying an uppermost wiring pattern layer carried by a semiconductor substrate. As a result, the heater elements can be arranged in closer proximity to liquid ink chambers, thus allowing efficient heat transfer from the heater elements to liquid ink chambers.
According to another aspect of the present invention, there are provided a printer, a printer head, or a method for fabricating a printer wherein heater elements are arranged so as to overlie a wiring pattern portion for power supplying or a wiring pattern portion for grounding, the wiring pattern portion being carried by a semiconductor substrate. As a result, the heater elements can be arranged in closer proximity to liquid ink chambers, as compared to a case in which the heater elements are arranged to underlie the wiring pattern portion. Accordingly, heat of the heater elements can be efficiently introduced to the liquid ink chambers, even when, for example, driving circuits are formed with multi-layer wiring.